1. Field of the Invention
The present invention relates to video projecting systems, and more particularly to video projecting systems for projecting an image which is generated from a video signal.
2. Description of the Background Art
There is a class of video projecting systems which project on a screen a number of partial images that are generated from a plurality of video projectors, so that a single stitched image is obtained on the screen. As shown in FIG. 12, a video projecting system of this kind typically includes video projectors 121 and 122 which are disposed side by side along the horizontal direction.
The video projector 121 includes a selector 1211, a scaling processing circuit 1212, a display device 1213, and an optical system 1214. The video projector 122 includes a selector 1221, a scaling processing circuit 1222, a display device 1223, and an optical system 1224.
Each of the selectors 1211 and 1221 includes a number of terminals (not shown). In the exemplary structure shown in FIG. 12, a first luminance adjustment circuit 123 and a third luminance adjustment circuit 125 are coupled to the respective terminals of the selector 1211. A second luminance adjustment circuit 124 and a fourth luminance adjustment circuit 126 are coupled to the respective terminals of the selector 1221.
Each of the scaling processing circuits 1212 and 1222 performs a scaling process as described below.
The display device 1213 includes on its display surface a number of pixels as specified by a given standard. The display devices 1213 and 1223 are usually produced so as to conform to the same standard or specifications.
The optical systems 1214 and 1224, each of which may be composed of a number of lenses, are disposed at a distance from the respective display surfaces of the display devices 1213 and 1223.
A screen 127 is disposed externally to the video projecting system, at a position away from the optical systems 1214 and 1224.
Now, an operation of the video projecting system will be described. First, a first video signal LFVS for the left-hand side and a first video signal RFVS for the right-hand side are supplied to the first luminance adjustment circuit 123 and the second luminance adjustment circuit 124, respectively. The first video signals LFVS and RFVS are generated from a first video signal FVS which represents a first image FV to be displayed.
The first video signal LFVS represents a first left partial image FLV, which defines a left-hand portion of the first image FV. The first video signal RFVS represents a first right partial image FRV, which defines a right-hand portion of the first image FV. When projecting the first image FV on the screen 127, the first left partial image FLV and the first right partial image FRV are employed in such a manner that the right vertical edge of first left partial image FLV and the left vertical edge of first right partial image FRV overlap each other, thereby obscuring the junction between the two partial images FLV and FRV.
The first video signal LFVS is received by the first luminance adjustment circuit 123. The first luminance adjustment circuit 123 attenuates a portion of the received first video signal LFVS, i.e., lowers the luminance of the overlapping region of the first left partial image FLV. It should be noted that the luminance of the non-overlapping region of the first left partial image FLV is not lowered. Thus, the first luminance adjustment circuit 123 transfers the processed first video signal LFVS to the selector 1211 as a first adjusted video signal ALFVS.
The second video signal RFVS is received by the second luminance adjustment circuit 124. The second luminance adjustment circuit 124 attenuates a portion of the received second video signal RFVS, i.e., lowers the luminance of only the overlapping region of the first right partial image FRV. The second luminance adjustment circuit 124 transfers the processed first video signal RFVS to the selector 1221 as the first adjusted video signal ARFVS.
The selector 1211 selects either the first luminance adjustment circuit 123 or the third luminance adjustment circuit 125. Assuming that the first luminance adjustment circuit 123 is being selected by the selector 1211, the first adjusted video signal ALFVS is passed through to the scaling processing circuit 1212.
The selector 1221 selects either the second luminance adjustment circuit 124 or the fourth luminance adjustment circuit 126. Note that when the first luminance adjustment circuit 123 is being selected by the selector 1211, the selector 1221 selects the second luminance adjustment circuit 124. In this case, the first adjusted video signal ALFVS is passed through to the scaling processing circuit 1222.
The scaling processing circuit 1212 applies a scaling process to the incoming first adjusted video signal ALFVS. The scaling process is performed because the first adjusted video signal ALFVS may not necessarily be of a signal format which conforms to the standard under which the display device 1213 is enabled to perform a display function. Accordingly, the scaling process is performed in order to convert the first adjusted video signal ALFVS so as to have a signal format which is displayable by the display device 1213. Typically, the original size (or the number of pixels contained) of the first left partial image FLV is converted to a size (or a number of pixels) which can be suitably displayed by the display device 1213. The first adjusted video signal ALFVS having been subjected to the scaling process is outputted to the display device 1213 as a first scaled video signal SLFVS.
The scaling processing circuit 1222 applies a scaling process (which is similar to that performed by the scaling processing circuit 1212) to the adjusted video signal ARFVS outputted from the selector 1221 so as to generate a first scaled video signal SRFVS to be displayed by the display device 1223, which is outputted to the display device 1223.
In accordance with the incoming first scaled video signal SLFVS, the display device 1213 generates the first left partial image FLV on the display surface. The generated first left partial image FLV is projected onto the screen 107 via the optical system 1214.
Similarly, in accordance with the incoming first scaled video signal SRFVS, the display device 1223 generates the first right partial image FRV. The generated first right partial image FRV is projected onto the screen 107 via the optical system 1224.
As a result of the aforementioned processes, the first left partial image FLV and the first right partial image FRV are projected on the screen 107 with a partial overlap therebetween. Thus, a viewer will perceive the first image FV, typically in an xe2x80x9clandscapexe2x80x9d shape, i.e., with greater horizontal length than vertical height. Furthermore, since the first luminance adjustment circuit 123 and the second luminance adjustment circuit 124 function to lower the luminance of the respective overlapping regions of the first left partial image FLV and the first right partial image FRV in the aforementioned manner, the overlapping region in the first image FV does not appear excessively bright as compared to the other regions. Thus, the conventional video projecting system displays the first image FV in a manner which appears substantially natural to the viewer despite the use of right and left partial images.
On the other hand, in the case where the video projecting system is employed to process a second video signal SVS which is of a signal format different from that of the first video signal FVS, and project a second image SV, the following sequence of processes is performed.
First, a second video signal LSVS for the left-hand side and a second video signal RSVS for the right-hand side, which are generated from the second video signal SVS representing the second image SV, are supplied to the third luminance adjustment circuit 125 and the fourth luminance adjustment circuit 126, respectively.
The third luminance adjustment circuit 125 attenuates some components of the received second video signal LSVS, i.e., lowers the luminance of only an overlapping region of the second left partial image SLV which the second video signal LSVS represents. The fourth luminance adjustment circuit 126 attenuates some components of the received second video signal RSVS, i.e., lowers the luminance of only an overlapping region of the second right partial image SRV which the second video signal RSVS represents.
The second video signals LSVS and RSVS having received the aforementioned processing are then transferred to the selectors 1211 and 1221 as second adjusted video signals ALSVS and ARSVS, respectively. The processes which are performed by the circuitry following the selectors 1211 and 1221 are similar to those described above with respect to the first image FV, and the descriptions thereof are omitted.
However, in accordance with the aforementioned conventional video projecting system, a corresponding number of luminance adjustment circuits are required for any number of signal formats used. Thus, there is a problem in that the overall system may experience a substantial increase in size, which in turn results in an increase in the cost required for constructing such a system.
Moreover, the use of the first video signal FVS and the second video signal SVS also invites the following problem in the aforementioned conventional system. Since the first video signal FVS and the second video signal SVS are of different signal formats, the width of the overlapping region between the first left partial image FLV and the first right partial image FRV may be slightly different from that between the second left partial image SLV and the second right partial image SRV. As a result, a viewer who wishes to view the first image FV and the second image SV one after the other, for example, may have to manually readjust the relative positions of the video projectors 121 and 102.
Therefore, an object of the present invention is to provide a compact and inexpensive video projecting system which can eliminate the need of the aforementioned manual readjustment.
In order to attain the aforementioned object, a first aspect of the present invention is directed to a video projecting system for generating a stitched image from partial images which are projected by a plurality of video projectors. Each of the plurality of video projectors comprises: a scaling processing circuit for applying a scaling process to an incoming video signal to generate a scaled video signal representing a partial image of a predetermined size; a luminance adjustment circuit for applying a luminance adjustment process to the scaled video signal which is outputted from the scaling processing circuit to generate an adjusted video signal representing the partial image having a reduced luminance in a predetermined region of the partial image; a display device for generating the partial image based on the adjusted video signal which is outputted from the luminance adjustment circuit; and an optical system for projecting the partial image generated by the display device. The partial images projected by the respective optical systems partially overlap each other so as to create the stitched image. The predetermined region is a region in which the respective partial images do overlap each other.